1. Field of Invention
This invention relates to a method and apparatus for refinishing a scratched optical surface on a compact disc. Specifically, heat is used to reflow the scratched optical surface of the disc, thereby allowing surrounding material to flow into and eliminate the scratches. The result is a reconditioned surface comparable to that found on a new compact disc.
2. Description of Prior Art
Numerous prior art patents have addressed the object of reconditioning scratched plastic surfaces. The need for such a process was realized long before the advent of the modern "compact disc." For example, U.S. Pat. No. 3,904,732 to Wick et. al. (1975) discloses a method for temporarily restoring optical clarity to scratched or glazed canopies on military helicopters. The Wick invention restores optical clarity by filling the scratches or voids in the canopy surface with a mixture of liquid tetrachloroethylene and trichloroethylene. The liquid mixture has a refractive index similar to the canopy itself, so that for as long as the liquid fills the voids, it renders the canopy clear. The effect is transitory, however, as the liquid does not remain in place for long.
Another method for refinishing a plastic surface is using vaporized solvents to reflow the surface and fill any voids. This method is disclosed in U.S. Pat. No. 4,247,580 to Chao (1981). The Chao invention uses an organic solvent, such as methyl ethyl ketone, to dissolve and reflow a thin layer of plastic on the surface of an object. While effective, the solvents required are highly volatile and are classified as environmental contaminants. Thus, the Chao invention may only be practiced in a contained environment under controlled circumstances.
Perhaps the simplest approach to restoring an optically clear surface is disclosed in U.S. Pat. No. 4,301,193 to Zuk (1981). The Zuk invention uses an abrasive composition applied with a polishing pad to cut away the optical surface until the scratches are removed and a new, smooth surface is revealed. A similar approach is disclosed in U.S. Pat. No. 5,334,335 to Norville (1994). The Norville process combines polishing with the use of organic solvents, representing a combination of prior art inventions.
Most of these prior art methods have been applied to compact discs. In U.S. Pat. No. 5,746,811 to Smithlin (1998), a waxy material, having a refractive index similar to the plastic found on compact discs, is used to fill scratches and voids. In U.S. Pat. No. 5,641,345 to Henry (1997), a polishing composition is used to remove the portion of the surface containing the scratches. U.S. Pat. No. 5,571,041 to Leikam (1996) also uses the polishing method, with the added step of applying a protective cover to the optical surface when the polishing is completed.
While these prior art methods can recondition the surface of a compact disc, they have several inherent limitations. For the wax fill method, the filler material tends to come loose over time, meaning that the compact disc performance will deteriorate. For the polishing methods, the surface of the disk must actually be abraded away, resulting in a thinner disc. The process may only be performed a few times before the disc is worn away. And, in the event of a deep scratch, the polish method takes a great deal of time to perform.
The method of using solvents to reflow and smooth the scratched optical surface requires dangerous chemicals, such as methyl ethyl ketone. With rising environmental concerns, the use of such volatile chemicals is becoming increasingly restricted.
Thus, the known methods for refinishing the optical surface of a compact disc are limited in that they wear away the surface of the disk, require the use of dangerous chemicals, require a long time to perform, fill only small scratches, only partially fill the scratches, or provide only a temporary remedy.